Seeing clearly: Understand binocular types before spending big

Understanding binoculars can be confusing. With so many brands and styles, how does one know which set is the right fit? The following should shed a little light on the topic.

Brandon Butler

Understanding binoculars can be confusing. With so many brands and styles, how does one know which set is the right fit? The following should shed a little light on the topic.

Body Style

There are two main body styles of binoculars: Porro prism and roof prism. Porro prism binoculars are offset, meaning the eye pieces and objective lenses are not in a straight line. The eye pieces are closer together than the objective lenses. Porro prism binoculars are the more traditional of the two styles. They are also, most often, the less-expensive style of binocular.

Roof prism binoculars are designed with the eye pieces and objective lenses in-line. In a pair of roof prism binoculars, the eye pieces and objective lenses share the same axis. One major advantage of roof prism binoculars is that they are usually less bulky. They are generally more expensive, though.

Both designs can provide excellent quality and enjoyable viewing. Determining which prism is right for you comes down to multiple factors, including cost, bulk and personal preference.

Optical Power

When shopping for a pair of binoculars, you’ll notice a mix of numbers. How do you know if you need 7x35, 8x42, 10x50 or 7-15x35?

The first number, to the left of the x, refers to magnification. If you were to purchase a set of 8x binoculars, you’d see an object eight times closer than it is. If you notice a number such as 7-15x, those binoculars have adjustable magnification.

The second number, the digit(s) to the right of the x, indicates how big the objective lens is. This represents how wide of a view the binocular has. It also determines how much light can be gathered to form an image. For example, an x50 will allow more light than an x28.

Quality of viewing generally depreciates with increased magnification. This is because of less light entering the lenses. The tradeoff for more power is often a less-clear image.

Glass

Binocular glass quality varies, so remember the golden rule of being a consumer; you usually get what you pay for.

BAK-4 prism glass and BK7 prism glass are commonly used to manufacture consumer-grade binoculars. Each offers light transmission and brightness, but they are not quite equal. BK7 is most often used on low- to mid-priced units, while general-purpose BAK-4 is used on higher-grade, more-expensive binoculars. BAK-4 is a softer glass, requiring more attention in grinding, thus offering greater light transmission and color correctness.

Lenses receive coatings to help reduce the amount of light, which is lost because of reflections. Generally, binoculars receive a single layer of coating on each glass surface. More-expensive models have multiple coatings, which reduces the amount of light lost to reflections.